The present invention relates in general to a control system for an internal combustion engine equipped at its exhaust section with a thermal reactor, and more particularly to a control system for regulating the engine exhaust gases fed into the thermal reactor in such a way that the reactor functions effectively.
Some modernized motor vehicles are equipped with thermal reactors in the exhaust sections of the internal combustion engines in order to completely burn out the remaining unburned combustible compounds such as hydrocarbons (HC) and carbon monoxide (CO) in exhaust gases emitted from the engines before the exhaust gases are discharged to the atmosphere.
In these thermal reactors, it has been recognized that, for achieving the effective combustion of the harmful combustible compounds mentioned above, it is necessary not only to maintain the exhaust gases fed into the reactor at highest possible temperature but also control the amounts of combustible compounds in the exhaust gases so that these combustible compounds can be effectively oxidized in the reactors.
As is well known, the temperature of the exhaust gases from the engine is severely and frequently changed in response to the various operating conditions of the engine thereby causing a difficulty in maintenance of the exhaust gases at the highest possible temperature. Thus, hitherto, the effective combustion of the combustible compounds in the thermal reactor has been achieved mainly by controlling the engine so as to produce exhaust gases containing considerably large amounts of hydrocarbons (HC) and carbon monoxide (CO). In reality, this exhaust contents control is made by feeding the engine with a relatively rich air-fuel mixture, for example, with the air-fuel ratio ranging from 11/1 to 14/1. (The stoichiometric air-fuel ratio of the mixture is about 14.8/1.)
With this procedure, it inevitably occures that the fuel economy of the subject system becomes worse due to the rich mixture combustion in a wasteful manner.
Furthermore, in this procedure, when the engine is subjected to a heavy load high speed operation during its working, there will arise a fear that the thermal reactor will be damaged or otherwise broken by the remarkably high heat generated in the thermal reactor. This is because the exhaust gases emitted from the heavily operating engine have in themselves considerably high temperature which promotes violent oxidation of the relatively large amounts of the remaining combustible compounds, so that the heat generated as a result of the combustion of the remaining combustible compounds in the thermal reactor becomes remarkably high. It is observed that the temperature in the thermal reactor used in the above-stated condition exceeds 1000.degree. C. very often.
If the thermal reactor is made of some heat resistant material to protect the same from the heat damage, the manufacturing cost is inevitably increased.